The present invention relates to a cathode ray tube and electron gun therefor, and, in particular, to a cathode ray tube and electron gun therefor including a conductively coated tube neck.
Color picture tubes are cathode ray tubes that typically include an electron gun producing three beams of electrons that are deflected by a magnetic deflection yoke to be raster scanned and to pass through apertures patterned in a shadow mask to impinge upon a faceplate or screen having a corresponding pattern of phosphors thereon. The pattern is of different phosphors that produce light of different colors, e.g., red, green and blue light producing phosphors, when impinged upon by a beam of electrons, i.e. each beam being for producing one of the three colors. Many conventional color tubes employing such three-beam electron guns are described in the following U.S. Patents:
U.S. Pat. No. 2,714,176 issued to Friend,
U.S. Pat. No. 2,726,347 issued to Benway,
U.S. Pat. No. 2,726,348 issued to Benway,
U.S. Pat. No. 2,861,208 issued to Benway,
U.S. Pat. No. 3,011,090 issued to Moodey,
U.S. Pat. No. 3,024,380 issued to Burdick et al,
U.S. Pat. No. 4,317,065 issued to Hughes,
U.S. Pat. No. 3,873,879 issued to Hughes,
U.S. Pat. No. 4,590,403 issued to Alig,
U.S. Pat. No. 4,614,894 issued to Izumida et al,
U.S. Pat. No. 4,945,284 issued to Shimoma, et. al,
U.S. Pat. No. 5,382,871 issued to Funahashi, et. al.
U.S. Pat. No. 5,488,265 issued to Chen
Three beam electron guns typically have three electron generating cathodes and a plurality of electron beam forming and focusing electrodes, each typically having three apertures through which the respective beams pass. Such beam forming electrode structures, which are also sometimes called electron lenses, sometimes have a single common opening through which the three beams pass, but have three-aperture plates through which the electrons enter and leave the lens.
Whether the three electron generating cathodes are in a triangular array, the so-called xe2x80x9cdeltaxe2x80x9d gun, or are in a straight side-by-side array, the so-called xe2x80x9cin-linexe2x80x9d gun, the electron beams travel through the various lenses along generally parallel trajectories and the apertures of each electrode are in the same array, either delta or in-line, as are the cathodes. An exception is the Trinitron electron gun which has common openings through which the three electron beams pass, but the three beams cross within the lens and must be redirected to the proper direction upon exiting the Trinitron lens.
The xe2x80x9cconventional wisdomxe2x80x9d is that electron guns require focus and anode grids with three-aperture electrode plates to converge and to focus the three beams. Moreover, it is usual that, as it is desired to xe2x80x9cimprovexe2x80x9d the electron gun, additional electrode structures be introduced to further shape and/or bend the electron beam. Thus, conventional electron guns tend to have a large number of metal electrodes or grids, including focus and anode grids.
Thus, it would be desirable to have an electron gun, and a cathode ray tube employing such gun, which does not require electrodes having a separate aperture for each electron beam, and that produces three electron beams that are substantially self converging to a single spot on the faceplate. It is also desirable that such electron gun, and a cathode ray tube employing such gun, have a larger diameter lens so as to reduce, or at least not increase, any aberration and spot distortion experienced by any of the electron beams.
To this end, the electron gun for producing at least three beams of electrons of the present invention comprises at least three electron sources for producing the at least three beams of electrons, a pre-focus lens for at least partly focusing each of the beams of electrons, and a main lens. According to one aspect of the invention, the main lens of the electron gun includes a hollow electrode for focusing and converging the at least three beams of electrons, the electrode having a non-uniform dimension iri the direction of electron travel therethrough thereby to define a substantially open non-planar exit aperture. According to another aspect of the invention, the main lens of the electron gun includes a hollow electrode for focusing and converging the at least three beams of electrons, the hollow electrode having an entrance and an exit opening, and an aperture plate intermediate the entrance and the exit opening, wherein the aperture plate has at least an elliptical center opening and two outer openings defined by two connected semi-ellipses through which respective ones of the at least three electron beams pass.